1. Field of the Invention
The present invention is broadly concerned with improved tamper-resistant switch assemblies operable to detect relative movement between first and second relatively shiftable members while providing a reliable anti-tampering feature. More particularly, the invention is concerned with such switch assemblies which are specifically designed for use in high security contexts, while permitting interior mounting of the components thereof within standard hollow door frames or the like.
2. Description of the Prior Art
In recent years the Magnasphere Corp. of Brookfield, Wis. has introduced a series of innovative and highly reliable switch products useful as a part of alarm systems or as proximity sensors. Such Magnasphere switches in general include a hollow housing typically (though not necessarily) formed of electrically conductive material and with one or more conductive electrodes extending into the housing. A shiftable conductive ball is also located within the housing. The ball moves under the influence of magnetic conditions between respective switch states, usually from a position of simultaneous contact with the switch electrodes to a position out of such simultaneous contact. Such switches are referred to herein as “magnetic ball” switches. U.S. Pat. Nos. 7,291,794; 5,977,873; 6,506,987; 6,603,378; 6,803,845; 7,023,308; and 5,332,992 illustrate various types of magnetic ball switches.
Harco Laboratories, Inc. of Bramford, Conn. has also commercialized a series of high-security switch products using multiple Magnasphere switches. See, e.g., U.S. Pat. Nos. 7,187,259; 7,218,194; and 7,248,136. High security switches of this type are almost always mounted externally, e.g., external assemblies are mounted in adjacent relationship on a door and door frame. These external switches may also include anti-tamper switch components, see U.S. Pat. No. 5,633,626.
However, externally mounted high security switches tend to be very unsightly and make easy access for potential tamperers. A particular problem in this regard is that putatively loyal employees may during business hours or other time when an alarm system is not operational attempt to tamper with inactive external switch components, so as to permit unauthorized entry during non-business hours when the alarm system is supposed to provide security.
Accordingly, there is a real unsatisfied need in the art for improved high security and other alarm switch assemblies which can if desired by mounted internally within hollow structures such as metallic door frames, and which provide reliable motion sensing and tamper sensing as required.